Well, the attorney for Chad and Lori pretty much sums it up - that they believe there is some action in play to take the children away from Lori and/or the investigations into the various deaths could result in charges and a conviction that would take Lori from them. I believe rather strongly that Lori does not want either child with Vallow or Ryan family members.
There have been a handful of cases involving missing Mormon children here at WS that involved either an actual custody dispute - especially loss of custody - or the potential of loss of custody and in every one I worked on there was at least several (up to more than two dozen) people that helped to hide the children from the courts, law enforcement, CPS, etc.
Lori has managed to get through more than two decades with children and not harm them so I do not believe that harm would suddenly manifest itself. It is entirely possible but I don't believe it to be the case here.